Foot orthotics can be fabricated by different techniques. Recently, additive fabrication/manufacturing techniques such as three-dimensional printing (3D printing) techniques have been used to fabricate foot orthotics, including customized foot orthotics. Additive manufacturing technology typically includes various processes to deposit, cure, fuse, or otherwise form layers in sequence to form a three-dimensional (3D) object.
For example, fused deposition modeling (FDM) technique, which is generally disclosed in U.S. Pat. Nos. 4,749,347 and 5,121,329, incorporated here by reference, include melting a filament of build material, extruding the print material out of an extrusion nozzle that is moved horizontally in the X and Y axes to deposit a thin melted and extruded print material on the previous layer where the new layer cools and hardens. These cross-sectional layers are stacked along the Z axis to form the 3D object. Most additive manufacturing processes need a base layer to print the next layer on top of it with a limited overhang.
In a typical 3D printing process, the printed object is supported on a bottom support. For fabrication of foot orthotics, the foot orthotics is typically printed bottom-up and the already printed material is supported from the bottom under the bottom surface of the foot orthotics. The rearfoot and forefoot postings have downward facing planar surfaces and are relatively easy to support. As the arch section of the foot orthotics also needs support, in some techniques, a temporary supporting raft with a curved top is first printed under the arch section of the foot orthotics and the foot orthotics is then printed on top of the supporting raft. The supporting raft and the foot orthotics may be printed with the same printing material, in which case it may be difficult to separate the supporting raft from the printed foot orthotics without leaving some surface defects or flaws on the printed foot orthotics. The supporting raft and the foot orthotics may also be printed with different printing materials, in which case the supporting raft may be more easily removed from the 3D printed foot orthotics, such as by mechanical or chemical means. Discrete supports, such as in the form of pillars or rib arrays, have also been used in some cases.
However, there are a number of drawbacks in such techniques. For example, printing the supporting raft requires both additional printing material and printing time. In some cases, the surface finish on the bottom surface of the resulting product is not smooth. When discrete supports are used, the bottom surface of the foot orthotics has portions that are not in contact with the supports, and these portions can still sag during the printing process. These factors tend to reduce the surface quality, surface finish and dimensional accuracy of the final product, and can increase the production failure rate.